Lubricating oil compositions of mixed diester dithiophosphates



Patented Sept. 14, 1954 LUBRICATING OIL COMPOSITIONS OF MIXED DIESTER DITHIOPHOSPHATES Paul K. Mulvany, Richmond, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application March 29, 1951,

Serial No. 218,282

Claims. 101. 252-32.?)

This invention pertains to a new composition of matter; that is, a lubricating oil composition comprising an oil of lubricating viscosity and zinc salts of mixed diesters of dithiophosphoric acids (i. e., wherein the organic portions of the acids are derived from two different alcohols e. g., butyl alcohol and hexyl alcohol). In particular, this invention pertains to lubricants containing zinc salts of mixed diesters of dithiophosphoric acids wherein the alcohols used in the preparation of the dithiophosphoric acids are of low molecular weight.

It is known that zinc salts of dialkyldithiophosphoric acids (wherein the alkyl groups are derived from the same alcohol) inhibit oxidation of lubricating oil compositions. It is also known that the alkyl groups of these zinc dialkyldithiophosphates may be of high molecular weight or low molecular weight. Zinc dialkyldithiophosphates, wherein the alkyl groups are the same and. each contain less than 6 carbon atoms (e. g., 4 carbon atoms), are considerably less expensive than the zinc dialkyldithiophosphates containing alkyl groups which are the same and derived from higher molecular weight alcohols. In spite of this, these zinc dialkyldithiophosphates having alkyl groups derived from low molecular weight alcohols (e. g., alcohols of l carbon atoms) have not been widely marketed as lubricating oil additives. The main reason for this has been the insufficient oil solubility of the zinc salts of low molecular weight dialkyldithiophosphoric acids to be able to prepare and market a concentrate in oil. This inability to ship concentrated oil solutions of these zinc salts due to the oil insolubility at normal storage conditions has more than offset the low cost of compounds per se.

It is a primary object of this invention to prepare lubricants containing zinc salts of mixed diester dithiophosphoric acids wherein the organo portions of the zinc salts are derived from two different low molecular weight alcohols, the zinc salts being soluble in oil to the extent of at least 35% at F.

It is a further object of this invention to provide lubricants containing zinc salts of mixed esters of dithiophosphoric acids in greater concentration than heretofore available.

These and further objects of this invention I will be apparent from the ensuing description and the appended claims.

It has been discovered that zinc salts of mixed esters of dithiophosphoric acids containing two dissimilar organo groups readily increase the useful life of lubricants. The lubricants considered herein comprise, in particular, oils of lubricating viscosity and zinc salts of mixed esters of dithiophosphoric acids.

The zinc salts of mixed esters of diothiophosphoric acids incorporated in the lubricating compositions of this invention are zinc salts of products obtained by reacting phosphorus pentasulfide with two different alcohols. I

One of the alcohols used in preparing the mixed ester of dithiophosphoric acids contains not more than 4 carbon atoms; for example, methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, sec-butyl alcohol and tertiary butyl alcohol. For convenience, this group of alcohols will hereinafter be called the R1 alcohols.

The other alcohols used in the preparation of mixed esters of dithiophosphoric acids contain from 6 to 18 carbon atoms. These include the following alcohols: hexyl, methylisobutylcarbinol, ethylisopropylcarbinol, heptyl, isoheptyl, 2-ethyl amyl, octyl, isooctyl, 3-ethyl hexyl, 2- propyl amyl, decyl, undecyl, dodecyl, hexadecyl, octadecyl, etc. For convenience, this group of alcohols will hereinafter be known as the R2 alcohols.

The R1 and R2 alcohols need not be present in the reaction mixture in equal molar amounts. For certain types of oils and for certain purposes it may be preferred that the mole ratio of R1 alcohols to R2 alcohols be from 1 to 5. It is particularly preferred to use a mole ratio of R1 alcohols to R2 alcohols from 2 to 4.

Suitable oils of lubricating viscosity include a wide variety of lubricating oils such as naphthenic base, parailin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., alkylene polymers (such as polymers of propylene, butylene, etc., and mixtures thereof), alkylene oxide type polymers, dicarboxylic acid esters and liquid esters of acids of phosphorus. Synthetic oils of the alkylene oxide type polymer which may be used include those exemplified by alkylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides (e. g., propylene oxide) in the presence of water or alcohols, e. g., ethyl alcohol, and esters of alkylene oxide-type olymers, e. g., acetylated propylene oxide polymers prepared by acetylating the propylene oxide polymers containing hydroxyl groups.

Synthetic oils of the dicarboxylic acid ester type include those which are prepared by esterifying such 'di'carboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alxenyl succinic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, Z-ethylhexyl alcohol, dodecyl alcohol, etc. Examples of dicarboxylic acid ester synthetic oils include dibutyl adipate, dihexyl adipate, di-2-ethylhexyl sebacat'e, di-n-hexyl fumarate polymer, etc.

Synthetic oils of the type of liquid esters of acids of phopshorus include the esters of phosphoric acid, e. g., tricresyl phosphate; the esters of phosphonic acid, e. g., diethyl ester of decane phosphonic acid, or other such esters as obtained by reacting alkyl phosphonyl chlorides with hydroxyl-containing compounds, such as phenols and aliphatic alcohols, and with olefin oxides such as propylene oxide, as described in Jensen et al., U. S. application Serial No. 86,856, filed April 11, 19 9, now abandoned.

The zinc salts of this invention; that is, the zinc salts of mixed esters of dithiophosphoric acids are normally used in lubricating oil compositions in amounts su'fiicient to inhibit oxida tion of the base oil. Although it is preferred to use from 0.05% to 2.0% by weight, based on the final oil composition, lubricating oil concentrates containing as much as 50% or more by weight may be prepared.

The zinc salts of this invention are formed from mixed esters of dithiophospho'ric acids prepared by reacting phosphorus pentasulfide (P285) with a mixture of two different alcohols at temperatures ranging from about 120 F. to 200 F. For example, in the preparation of mixed esters of dithiophosphoric acids wherein methyl alcohol and hexyl alcohols are the two alcohols, 4 moles of the desired alcohols (e. g., 3 moles of methyl alcohol and 1 mole of hexyl alcohol, wherein the mol ratio of methyl alcohol to hexyl alcohol is 3:1) are reacted with 1 mole of PzSs at temperatures ranging from about 120 F. to 180 F. for a time sufficient to complete the formation of methyl hexyl dithiophosphoric acid. In the preparation or the zinc salts of the mixed dialkyldithiophosphoric acids (e. g., zinc methyl hexyl dithiophosphate), the mixed dialkyldithiophoshphoric acids are reacted with zinc oxide at temperatures ranging from 70 F. to 170 F.

The following examples illustrate methods of preparing zinc salts of mixed esters of dithiophosphoric acids.

Example 1.Zinc salt of reactionproduct of isopropyl alcohol, methylisobutylcarbinol and P285 A mixture of 252 parts by weight (67 mole per cent) of isopropyl alcohol and 206 parts by weight (33 mole per cent) of methylisobutylcarbinol was placed in a glass reaction vessel. To this mixture was added 333 partsby weight of P265. The whole mixture was heated at 170 F. for 2 hours, after which the reaction mixture was cooled, and the product filtered to remove a small amount of unreacted P2S5.

650 grams of the acid intermediate thus obtained was added to 130 parts by weight of a petroleum oil having a viscosity of 300 SSU at F. (used as a diluent), then 122 parts by weight of zinc oxide was gradually added at F. The whole mixture was then agitated for 3 hours at 130 F., after which the water of neutralization Was removed with calcium sulfate. The oil solution of the zinc salt had a pH of 6.7 (after filtration) and contained 9.96% zinc, 9.43% phosphorus and 19.42% sulfur.

Example 2.--Zinc salt of reaction product of butyl alcohol, methylisobutylcarbinol and PzSs A mixture of 237 parts by weight (77 mol per cent) of sec-butyl alcohol, 98 parts by weight (23 mole per cent) of methylisobutylcarbinol and 222 parts by weight of P285 was charged to a reaction vessel and agitated at F. for a period of 2 hours. The reaction mixture was cooled and filtered to remove a small amount of unreacted P285. The resulting butylmethylisobutylcarbinol dithiophosphate was a dark red green liquid having a neutralization number of 193 (mgs. KOH/gram) a viscosity of 35.7 SSU at 100 F., a specific gravity of 1.04 (60/60), and contained 24.0% sulfur and 11.9% phosphorus.

To the above mixture was added 8'! parts by weight of zinc oxide, after which the whole was heated with agitation at 130 F. for 4 hours until a pH of 6.7 was reached. After the water of neutralization had been removed, the oil solution contained 7.6% zinc, 7.2% phosphorus and 15.0% sulfur.

The oil solubility of mixed diester dithiophosphoric acids, having certain mole ratios of 1 ester group to the other ester group (and the corresponding zinc salts), is considerably greater than the same mole ratio of a mixture of two diester dithiophosphoric acids (wherein the ester groups in each acid are the same; that is, each acid contains only one of the ester radicals of the above mixed diester dithiophosphoric acid). For example, a 35% petroleum oil solution of a mixture of zinc di(sec-butyl) dithiophosphate and zinc di(methylisobutylcarbinol) dithiophosphate (mole ratio of 3.35:1) began to crystallize from solution within a period of 2 days at -20 F. On the other hand, an 81% oil solution (same oil as above) of zinc sec-butyl methylisobutylcarbinol dithiophosphate (prepared according to Example 2 above) was still clear after 30 days at 20 F. Similarly, an 8% petroleum oil solution of a mixture of zinc diisopropyldithiophosphate and zinc di(methylisobutylcarbinol) dithiophosphate (mole ratio of 2:1) began to crystallize from solution within 3 days at +30 F. However, an 85% petroleum oil solution of zinc isopropyl methylisobutylcarbinol dithiophosphate prepared as in above Example 1 did not show any signs of crystallization after 34 days at +30 F.

The table below presents data concerning the effectiveness of zinc salts of mixed esters of dithiophosphoric acids in reducing corrosion of metal parts due to oxidation of lubricating oils during operation of internal combustion engines. To obtain these data, a stock Chevrolet engine was used. Instead of the normal babbitt bearings of the Chevrolet engine, two of the connecting rods were modified to accommodate copper-lead bearing inserts, Which were weighed before being assembled in the engine. The Chevro et engine was operated at 3150 R. P. M., the engine jacket temperature was maintained at 200 F., the crankcase oil temperature was maintained at 280 F., and the engine was operated for a period of 36 hours before being disassembled and the bearing inserts weighed. Before weighing, the bearing inserts were carefully washed with solvents to remove the oil therefrom.

=This reference oil was a California solvent-refined paralfinic base SAE 30 011 containing 0.80% by weight of a calcium alkyl sulfofiiatetand 0.97% by weight of a suL urizcd alkyl-substituted calcium p vli eizht loss after hours.

a Prepared as in Example II above.

d This reference 011 was a Mid-Continent SAE 30 oil.

Tests were also run to determine the effectiveness of the zinc salts of mixed diesters of dithiophosphoric acids for increasing the inhibition period of lubricating oils. A medicinal white oil was the base oil. The inhibition period (the time in hours before 100 grams of oil sample utilizes 1000 cubic centimeters of oxygen at 340 F.) of medicinal white oil was zero hours. The inhibition period of the same base oil containing 0.19% of the zinc salt of Example 2 above was 4.2 hours.

Other uses of the zinc salts of mixed esters of this invention also include phenates (e. g'., calcium cetyl phenate), sulfonates (e. g., calcium petroleum sulfonate), phenols (e. g., 2,6-di-tertiary butyl-4-methyl phenol), phosphonates (e. g., calcium white oil phosphonate), thiophosphonates (e. g., calcium cetyl thiophosphonate), sulfur-containing parafiins (e. g., sulfurized diparaffin sulfide), etc.

I claim:

1. A lubricant consisting essentially of a major proportion of an oil of lubricating viscosity and from 0.05% to 2.0% of zinc salts of mixed esters of dithiophosphoric acids produced by reacting phosphorus pentasulfide with a blend of 2 aliphatic monohydric alcohols at temperatures from F. to 200 F., one of said alcohols containing not more than 4 carbon atoms, the other of said alcohols containing from 6 to 18 carbon atoms, the ratio of the lower molecular weight alcohol to the higher molecular weight alcohol being from 1.0 to 5.0.

2. The lubricant of claim 1, wherein a butyl alcohol and a hexyl alcohol are used in the preparation of the mixed esters of dithiophosphoric acids.

3. The lubricant of claim 1, wherein secondary butyl alcohol and methylisobutylcarbinol are used in the preparation of the mixed esters of dithiophosphoric acids.

4. The lubricant of claim 1, wherein isopropyl alcohol and methylisobutylcarbinol are used in the preparation of the mixed esters of dithiophosphoric acids.

5. A lubricating oil composition comprising a major proportion of an oil of lubricating viscosity and from 0.05% to 2.0% of zinc salts of mixed esters of dithiophosphoric acids produced by reacting phosphorus pentasulfide with a blend of 2 aliphatic monohydric alcohols at temperatures from 120 F. to 200 F., one of said alcohols containing not more than 4 carbon atoms, the other of said alcohols containing from 6 to 10 carbon atoms, the ratio of the lower molecular weight alcohol to the higher molecular weight of alcohol being from 1.0 to 5.0.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,342,432 Smith et al Feb. 22, 1944 2,334,393 Cook et a1. Mar. 14, 1944 2,368,000 Cook et a1 Jan. 23, 1945 

1. A LUBRICANT CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF AN OIL OF LUBRICATING VISCOSITY AND FROM 0.05% TO 2.0% OF ZINC SALTS OF MIXED ESTERS OF DITHIOPHOSPHORIC ACIDS PRODUCED BY REACTING PHOSPHORUS PENTASULFIDE WITH A BLEND OF 2 ALIPHATIC MONOHYDRIC ALCOHOLS AT TEMPERATURES FROM 120* F. TO 200* F., ONE OF SAID ALCOHOLS CONTAINING NOT MORE THAN 4 CARBON ATOMS, THE OTHER OF SAID ALCOHOLS CONTAINING FROM 6 TO 18 CARBON ATOMS, THE RATIO OF THE LOWER MOELCULAR WEIGHT ALCOHOL TO THE HIGHER MOLECULAR WEIGHT ALCOHOL BEING FROM 1.0 TO 5.0. 